1. Field of the Invention
The invention relates to a tunable toolholder for suppressing vibrations caused in the machining processes and, more particularly, to a tunable toolholder which utilizes a dynamic vibration absorber to suppress vibrations.
2. Description of Related Art
During a metal cutting operation, any vibration between a cutting tool and a workpiece may lead to undesirable cutting performances, such as poor workpiece surface finish and out-of-tolerance finished workpieces. Furthermore, such vibration may cause the cutting tool, or the associated machine tool, to become damaged.
To reduce this vibration, the metal removal rate can be decreased. However, this approach interferes with production and only minimally reduces the amount of vibration.
The cutting tool is typically secured within a toolholder. Attempts to eliminate the vibration in the toolholder, such as a boring bar, may include using a boring bar fabricated from solid carbide. Solid carbide, because of its inherently high density, reduces the amount of chatter and vibration transferred to the boring bar. However, solid carbide is extremely expensive. Furthermore, although chatter and vibration are reduced by the inherently high density of the solid carbide bar, vibration nonetheless may build up to an unacceptable level. Still furthermore, solid carbide is fairly brittle and a minor impact upon the boring bar during use or setup may inadvertently damage the bar.
Other attempts to reduce vibration in boring bars include mounting upon or within the bar a dynamic vibration absorber, such as that absorber disclosed in U.S. Pat. No. 3,774,730, which is comprised of a cylindrical mass of a high density material supported on rubber bushings. When optimally tuned, the mass oscillates in response to the vibration produced in the boring bar to cancel out vibration. The absorber may be tuned to accommodate the boring bar for the speed at which the workpiece or boring bar is rotating, the length of the boring bar, and the type of cutting tool connected at the end of the bar. Such an adjustment is made by longitudinally urging pressure plates at opposing ends of the cylindrical mass, thereby compressing the rubber bushings against the mass. This simultaneously shifts the position of the mass and alters the stiffness of the rubber bushings to change the dynamics of the bar.
Typically, the adjustment of the pressure plates is made from the rear of a boring bar as illustrated in U.S. Pat. No. 3,838,936 or from the side of the toolholder, as illustrated in FIG. 1 of U.S. Pat. No. 5,518,347.
While these mechanisms may be suitable for toolholders and boring bars having relatively large diameters, when a toolholder has a small diameter, such as, for example, less than one inch, then because of space limitations, access from the rear of the toolholder, or from the side of the toolholder, may become difficult and passageways providing such access may substantially weaken the boring bar structure.
U.S. Pat. No. 5,518,347 (the ""347 patent) is also directed to a tuned damping system for an end mill, wherein a tuning fixture has a longitudinally oriented adjusting screw to apply force against elastomeric supports, which act against a damper mass. However, after adjusting the supports against the mass, the tuning fixture must be removed and replaced with a cutting head to perform various cutting tasks. The damper mass is kept in compression after removal of the tuning fixture by a clamping screw, which locks the system adjustment in place. While the cutting head is in place, the tuning of the system is fixed and may not be adjusted further.
The system disclosed in the ""347 patent permits front adjustment of the supports, but does so in a fashion that creates yet another disadvantage. The tuning fixture is placed on the end mill during a tuning operation and, once the system is tuned utilizing the tuning fixture, the clamp screw must be secured and the tuning fixture removed and replaced with an appropriate cutting head. The tuning fixture is sized such that the mass is very near to the mass of the cutting head to simulate the presence of the cutting head during a machining operation. As a result, if a different cutting head were to be used, then a different tuning fixture having a different mass would be required.
A toolholder used for metalworking operations has a shank having a front end, back end and a longitudinal axis, wherein a cavity extends within the shank along the axis and wherein the cavity defines a cavity wall. An absorber mass is positioned within the cavity, wherein the mass has a first end and a second end. A resilient support circumscribes each end of the mass and is positioned to suspend the mass within the cavity. There is a pressure plate at each end of the absorber mass adjacent to each resilient support, wherein at least one pressure plate is movable along the longitudinal axis to compress each resilient support against the absorber mass. A toolholder head has a pocket adapted to receive a cutting tool and furthermore has a front face and a rear face, wherein the head is secured at the rear face to the front end of the shank. An adjustment screw extends through the front face of the toolholder head and is oriented to displace the movable pressure plate along the longitudinal axis within a desired range against the resilient support at the first end of the shank.